1. Field of the Invention
The present invention relates to a so-called hybrid-type display apparatus (hereinafter referred to as a semi-transmission reflection layer) provided with a reflection layer having a hole in part on its rear side (hereinafter referred to as a semi-transmission reflection layer).
2. Description of the Related Art
A hybrid-type display apparatus is disclosed, for example, in Japanese Patent Application Publication Laid Open Nos. 11-052366 and 11-183892. In a hybrid-type liquid crystal display apparatus, when there is external light (natural rays of light, indoor illumination or the like) that ensures a sufficient brightness can be obtained, it performs a transmission-mode display that utilizes the external light by reflecting its external incident light entering from a front side on a semi-transmission reflection layer on the rear side; and, when any external light ensuring a sufficient brightness is not obtainable, it performs a transmission-mode display that utilizes rays of light from a back-light disposed on the rear side of the liquid crystal display apparatus. This hybrid-type liquid crystal display apparatus is comprised of: a pair of substrates disposed in opposite directions on the front and rear sides; an electrode provided on an internal surface of one of the pair of substrates; an electrode provided on an internal surface of the other one of the pair of substrates; a liquid crystal layer interposed between said pair of the substrates; and a semi-transmission reflection layer provided on the rear side thereof.
As a liquid crystal display apparatus, there are many types including an active-matrix type, a simple-matrix type and the like. For example, a liquid crystal display apparatus of the active-matrix type is comprised of: a plurality of pixel electrodes arranged in a matrix form on an internal surface of a first substrate; a plurality of active elements connected with these pixel electrodes respectively; a signal line for supplying a signal to said plurality of active elements; counter electrodes provided on an internal surface of a second substrate, disposed opposite to said plurality of pixel electrodes; and a region of a pixel in which said plurality of pixel electrodes and said counter electrodes are opposed to each other.
Further, as other types of the liquid crystal display apparatus, there are one that displays white and black pictures and another that displays color pictures. In a liquid crystal display apparatus that displays a multi-color picture, such as a full color image or the like, there are provided colored films of a plurality of colors, each having a different transmission wavelength band provided on an internal surface of its front side (first) substrate, and each corresponding to a plurality of pixels having a pixel electrode and a counter electrode disposed in opposite directions. Normally, these colored films are color filters of red, green and blue, and each color filter is formed to have the same area as that of its pixel in order to ensure that the whole light passing through the pixel and emitted as a colored light has good color purity.
However, the hybrid-type liquid crystal display apparatus having prior art filters has the problem that its display according to its reflection display mode using an external light source is very dark. This is mainly due to light absorption in the color filter. Because a color filter allows rays of light to pass in a wavelength band corresponding to the color of its color filter among visible rays of bands and absorbs rays of light in the other wavelength bands, the intensity of colored light having passed the color filter is decreased substantially in comparison with the intensity of incident light.
Further, in the case of the hybrid-type liquid crystal display apparatus, a drop in brightness of the display at the time of performing a transmission-mode display utilizing a light from a back-light; can be compensated by increasing the brightness of the back-light, however, when performing a reflection-mode display utilizing an external light, such a high brightness incident light that can compensate for the absorption of light in the color filter cannot be obtained. Further, because the incident light entering the liquid crystal display apparatus from its front side passes through the color filter twice before it is reflected on the semi-transmission reflection layer on the rear side and emitted toward the front side, its absorption of light increases further, thereby darkening the display substantially.
Therefore, there has been proposed to decreasing the absorption of light in the color filter and improving the brightness of the display by reducing the film thickness of the color filter. However, because this reduction in film thickness of the color filter causes the transmission of light in its absorption wavelength band to increase as well, a colored light having a good color purity becomes impossible to obtain, thereby resulting in a narrowed color range of color pictures to be displayed.
A hybrid-type display apparatus that improves the lightness of color (reflectance) availed in the case of a reflection display while on the other hand maintaining the color purity availed in the case of a transmission display has been proposed. FIGS. 5A and 5B show schematic diagrams of such a hybrid-type display apparatus. FIG. 5A shows a planer pattern thereof corresponding to one pixel. As shown in the drawing, a pixel PXL is divided on its plane into a transmission portion T that corresponds to a hole of a semi-transmission reflection layer and a reflection portion R that is outside the hole. Although a color filter CF is provided to cover the whole area of the transmission portion T, it covers only partially the reflection portion R. Namely, in contrast to the pixel PXL that is patterned into a rectangle, the color filter CF is patterned into a hexagon, as shown in the drawing, with the color filter CF removed partly from each corner of the reflection portion R. Thereby, while ensuring that the transmission portion T is able to obtain sufficient color purity, it is arranged for the reflection portion R to have a mixture of colored light passing through the color filter CF and non-colored light not passing therethrough so as to improve the lightness of the color.
FIG. 5B is a cross-sectional diagram of a related art cut out along the line VB-VB shown in FIG. 5A. On an internal surface of a front side substrate 1, there is formed the color filter CF patterned into a hexagon. On an internal surface of a rear side substrate 2, there is formed a reflection layer 8 of semi-transmission type having a hole H. Between both the substrates 1 and 2, there is retained a liquid crystal layer 3 as an electro-optical layer. A portion corresponding to the hole H of the semi-transmission reflection layer 8 becomes the transmission portion T of the pixel and the other portions become the reflection portion R. As to the transmission portion T, an incident light from the back light and through the rear side substrate 2 passes the color filter CF once and arrives at an observer positioned in front of the front side substrate 1. As to the reflection portion R, an incident light entering from the observer side is reflected on the reflection layer 8 and is directed toward the observer again. At this time, a part of the incident light passes a cutout portion devoid of the color filter CF, is reflected on the reflection layer 8, and then passes a portion where the color filter CF is positioned. At this time, because its external light is caused to pass through the color filter CF only once in the same manner as in the case of the backlight, the absorption is weakened, thereby improving the lightness of the color and ensuring a preferred reflectance is obtained.
However, there is the problem associated with the prior art that when patterning the color filter CF into a hexagon as shown in the drawing, because of the difference from the rectangular boundary of the pixel PXL, a cutout portion of the color filter CF may be identified sometimes as a pixel defect. Further, the irregular patterning of the color filter CF, such as into a hexagon, also involves a the problem of increasing the proportion of defective patterning.
It is therefore an object of the present invention to solve the problems associated with the prior art and to provide an improved hybrid-display apparatus.
In order to solve the above-mentioned problem associated with the prior art, the following measures have been taken. Namely, the display apparatus according to the present invention is comprised basically of: a pair of substrates, a first substrate on a front side and a second substrate on a rear side, disposed in opposite directions from each other; a first electrode provided on an internal surface of the first substrate; a second electrode provided on an internal surface of the second substrate; a color filter provided on the second substrate on the rear side and aligned with a pixel that is defined between the above-mentioned first electrode and the above-mentioned second electrode disposed in opposite directions; an electro-optical layer interposed between the above-mentioned pair of substrates; and a reflection layer provided on the second substrate on the rear side. Here, the above-mentioned reflection layer has a hole provided for each pixel, which divides a plane of each pixel into a transmission portion, which is within the hole, and a reflection portion, which is outside the hole. The above-mentioned color filter is comprised of a lamination of a colored layer and a transparent layer. As features according to the present invention, the above-mentioned colored layer is formed to be thinner in the reflection portion than in the transmission portion, and the above-mentioned transparent layer is formed to cover a difference in level of the colored layer caused between the transmission portion and the reflection portion.
Preferably, a thickness of the above-mentioned transparent layer is set at an optimum value such that an optical density of the colored layer is adjusted between the transmission portion and the reflection portion. According to a preferred embodiment of the present invention, the above-mentioned transparent layer is comprised of a transparent resin film that is formed in an internal surface of the first substrate on the front side, and the colored layer is comprised of a colored film that is formed so as to overlap the transparent resin film. According to another preferred embodiment of the present invention, the above-mentioned transparent layer is formed by selectively etching the internal surface of the front side substrate, which is transparent, and the colored layer is provided by a colored film that is formed on the internal surface that is etched as described above. Preferably, the above-mentioned electro-optical layer is comprised of a liquid crystal layer having a birefringence property, and its thickness is set twofold in the transmission portion than in the reflection portion. Preferably, the above-mentioned first electrode is a common electrode formed in common across pixels, and the above-mentioned second electrode is a pixel electrode that is isolated for each pixel, and on the second substrate there is formed an active element for driving its pixel electrode.
In the hybrid type display apparatus according to the present invention, in the process of forming the color filter, its transparent layer is formed only in its reflection portion, and then its colored layer is formed thereon. Thereby, it can reduce the thickness of the colored layer in the reflection portion than in the transmission portion by a thickness of the transparent layer that is included therein. Therefore, absorption in the color filter in the reflection portion is reduced, and lightness of color is substantially improved and its reflectance is increased. On the other hand, as for the transmission portion, because its colored layer is ensured to have a sufficient thickness, it enables a preferred color purity (optical density) to be obtained. By optimization of a film thickness of the transparent layer, it becomes possible, without impairing the color purity of the transmission type, to specify a reflectance and color purity of the reflection type at a preferred value. The colored layer itself of the color filter can be patterned in alignment with its pixel thereby causing no deformation, no pixel defect or the like to occur.